T&ecirc;te-&agrave;-T&ecirc;te: the lives and loves of Simone de Beauvoir and Jean-Paul Sartre, by Hazel Rowley

They were the 20th-century Godwin and Wollstonecraft, philosopher and feminist, united but free. Jean-Paul Sartre and Simone de Beauvoir knew that their relationship was the stuff of legend and assiduously cultivated the myth. They met as part of a brilliant group of students at the Ecole Normale and embarked on a love affair that would last for the rest of their lives. Intellectual equals - in the highly competitive examination for the philosophy agregation they passed first and second in their year, out of all the students in France - they would not be shackled by any formal ties, but would make their own lives the model for a new kind of partnership between the sexes, one that would leave them free to fall in love with others, but so secure in their own love and so honest in their dealings that there would be no question of jealousy between them. How this pact worked out is Hazel Rowley's subject and makes, as she says, "a great story... exactly what Sartre and Beauvoir always wanted their lives to be".

Myths, however, are constantly open to reinterpretation and this one has already undergone some revisions since the deaths of Sartre in 1980 and de Beauvoir six years later. Some feminists had already argued that in this relationship of equals one was more equal than the other: that the pact of free love worked, in a man's world, to de Beauvoir's disadvantage. Then the publication of their correspondence (or part of it) revealed the extent to which she had encouraged his affairs with young women, and for some critics this made the pair seem less like Godwin and Wollstonecraft than like the scheming Valmont and Merteuil in Laclos's Liaisons dangereuses. They told one another everything (which does not mean, as Hazel Rowley points out more than once, that they did not frequently lie to each other as well); and their refusal to commit fully to anyone else inevitably meant disappointment and unhappiness for some of their other partners, who had to pay the price of their freedom.

While insisting that this is not a biography, Rowley follows the lives of her two subjects more or less chronologically, from schooldays to death. She sketches in the historical background: teaching in the troubled 1930s; the dramas of war, resistance and occupation; the heady days of postwar existentialism; the political commitments of the Cold War era; the glorious 1960s; Sartre's Maoist 1970s and the sad last years. Along the way she mentions the literary works that occupied the greater part of her subjects' time: Sartre, in particular, had a gruelling schedule of writing: philosophy, fiction, plays, criticism and huge amounts of journalism, as well as the many letters on which part of this account is based, fuelled by does of corydrane, whisky and Boyard cigarettes. In this daily round, his women occupied designated hours and days of the week, taking up rather little of his time, especially once a relationship was established. Readers may applaud Rowley's decision to give us the sex without too much of the duller stuff in between, but even she makes it clear that both Sartre and de Beauvoir mostly had other things on their minds.

As existentialists, they were also, inevitably, much aware of their responsibilities. Sartre often felt guilty towards his women, grateful to them for loving him (he was very conscious of his own ugliness), and generous towards them with money and other kinds of support (for example, giving them roles in productions of his plays). The Sartre-Beauvoir concept of the just life may not have been that of conventional society, but it was not unprincipled or unconsidered. Those who believe that de Beauvoir came out worse from the deal may be right: despite her image as a bit of a cold fish, she spends a good deal of time here in tears. But she also left no doubt that her life was freely chosen and fulfilling.

In her account of it, Rowley draws extensively on de Beauvoir's autobiographies, on Sartre's account of his intellectual development in Les Mots, on their published correspondence and on interviews with those who knew them. The illustrations are well-chosen, including the rather touching 1950 photograph of de Beauvoir's back, taken during her affair with the American writer Nelson Algren, as she stands doing her hair in a bathroom mirror, wearing only a pair of high-heeled shoes. No doubt, there are further revelations to come: Rowley describes the difficulties she met when trying to obtain materials from Sartre's literary executrix, Arlette Elkaim, and there is a quantity of unpublished letters, journals and other writings. But, if this is not the whole story, it is surely correct in the main, as well as sympathetic to these two brilliant, sometimes misguided, always interesting people, whose enduring love for each other was not the least of their achievements.

Robin Buss is the translator of a selection of Sartre's writings, 'Modern Times', published by Penguin Modern Classics